1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a method and apparatus for pressing base plates into actuator arms.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or "gram load". Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load.
A head-carrying suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. The combined base plate, load beam and a flexure make up a head suspension, and the suspension has the hub of the base plate extending through and beyond the load beam clearance hole.
The hubs of two suspensions are inserted into an actuator arm boss hole formed through an actuator arm extending from an actuator body, one hub entering an actuator arm boss hole from each end of the hole. In the prior art, a swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss hole. Thus, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
Problems with this method of mounting transducer heads have arisen as the need for increased data storage capacity in hard disk drives has grown and the size of the disk drive has decreased to fit in small lap top computers. The problem of forming a strong connection between the actuator arms and the transducer suspensions has been made more difficult as the thickness of the components has become smaller.
Because of the joining of two transducer suspensions to an actuator arm by passing a swage ball through two hubs in the same hole in the actuator arm, an asymmetry exists in the forces that are exerted on the hubs to make the joints. Because the transducer heads face in opposite directions, the suspensions and therefore the hubs on their respective load beams also extend in opposite directions with respect to the direction of passage of the ball through the inner diameters of the hubs. For one transducer suspension, the ball is passed in a direction that tends to place the hub in compressive stress while, for the other transducer suspension, the direction of passage of the ball is such as to tend to place the hub in tensile stress. In order to achieve a permanent bond between the hub and the actuator, the passage lo of the ball must cause permanent, or plastic, deformation of the hub. This deformation often causes a change in shape of the flange portion of the base plate, is which results in a change in the suspension gram load. The differences in shape changes and stresses between the suspensions swaged in tension and compression causes differences in gram load change and hub/actuator joint integrity between these up and down facing suspensions.
It is an object of this invention to provide a method and apparatus for use in assembling a disk drive that eliminates the need for swaging and the resulting up and down facing head pre-load and joint integrity differences.
It is also an object of this invention to provide a method and apparatus for use in assembling a disk drive that presses base plates into actuator arms thereby creating a press fit.
It is also an object of this invention is to provide a method and apparatus for use with novel base plates that can be pressed into an actuator arm to create a press fit.
The above-referenced co-pending application Ser. No. 09/003,871 discloses a novel base plate for press fitting into a boss hole of a predetermined nominal diameter. The base plate has a flange and a hub extending from a region at which the hub meets the flange to an outer end of the hub. The hub has a number of vertical slots cut through the hub extending from the outer end of the hub part way or all the way to the region at which the hub meets the flange, a space between slots determining boundaries of a prong. The hub has an outer diameter which is greater than the predetermined nominal diameter. Alternatively the hub has an outer diameter at the region at which the hub meets the flange which is not greater than the predetermined nominal diameter, in which case each prong extends outward to a prong outer diameter which is greater than the predetermined nominal diameter. Also the base plate may have a corner relief that circumscribes the region at which the hub meets the flange.
The above-referenced co-pending application Ser. No. 09/002,068 also discloses a base plate for press fitting into an actuator arm boss hole of a predetermined nominal diameter. In this instance, the hub has a number of vertical teeth protruding from the hub extending from the outer end of the hub to the region at which the hub meets the flange. The hub has an outer diameter which is greater than the predetermined nominal diameter of the actuator arm boss hole. A corner relief may be provided that circumscribes the region at which the hub meets the flange.
Copending application Ser. No. 08/943377 discloses a base plate that has a flange and a hub that is formed with a fold portion extruded from the flange which extends beyond an outer diameter of the hub to form a barb. Since the fold extends outward to increase the outer diameter of the hub by forming a barb, this allows a press fit, thrusting the barb into the arm material, thereby eliminating the need to swage.
As more fully described in the above identified copending applications, the base plates are designed to be pressed into tight engagement with the inner peripheries of an actuator arm boss hole without swaging. An actuator body with arms extending therefrom resembles the letter "E" and hence is called an "E-block". In practice, a disk drive will have several actuator arms, with the hubs of two suspensions inserted into actuator arm boss holes formed through a plurality of actuator arms extending from the actuator body. In the middle arms of the actuator, one hub enters an actuator arm boss hole from each end of the hole. Therefore, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
It is therefore also an object of this invention is to provide method and apparatus for use with base plates that can be pressed into actuator arms of an actuator body to create a press fit.